It is often desirable to provide absorbent articles of the above-mentioned type with functions going beyond their capacity to absorb and store body fluids such as urine or menstrual fluids. These functions involve for instance a skin care effect or the suppression or prevention of unpleasant odours.
Existing absorbent articles that show these additional functions comprise active agents, which are either loosely bound to a diaper part or embedded in a matrix being typically of lotion type (see for instance WO 96/16682) or polymer type.
Loosely bound active agents suffer from the disadvantage that they are too easily rubbed off or washed off under body motion or with the first gush of urine. This may also occur if the active agent is fixed in a lotion matrix. Polymer systems, on the other hand, are often not capable of releasing active agents specifically when these are needed, that is upon contact with body fluids. Moreover, relatively high amounts of polymers or lotions are needed for an efficient embedding of the active agent. Polymers and lotions can also adversely affect the properties of the underlying substrate such as flexibility, softness, absorbency, hydrophilicity, etc.
Moreover, nanoscalar films of self-assembling polymers are known from various technical fields and have attracted considerable interest over the last years. These nanoscalar films are typically formed by the alternate deposition of monomolecular layers of two polymers having functional groups capable of interacting with each other. A great deal of these studies has been conducted with the layer-by-layer deposition (also abbreviated as LBL deposition) of cationic and anionic polymers based on the reversal of the surface charge after each deposition, one of the best-examined systems being poly(styrene sulfonate)/(polyallylamine hydrochloride)(PSS/PAH).
U.S. 2005/0069950 A1 discloses a method for the nanofabrication of thin films, coatings and microcapsules based on suitable design of oligopeptides. Drug delivery is discussed in connection with microcapsules. Moreover, disposable diapers are mentioned as one among many possible uses for peptides designed according to this documents. More concretely described are biomedical applications.
U.S. Pat. No. 5,807,636, U.S. Pat. No. 5,700,559 and U.S. Pat. No. 5,837,377 relate to a hydrophilic article for use in aqueous environments including a substrate, an ionic polymeric layer on said substrate and a disordered polyelectrolyte coating ionically bonded to said polymeric layer. Diapers and other liners are mentioned as one among many potential applications of this teaching.
WO 2005/058199 relates to an electrostatically self-assembled antimicrobial coating for medical applications, in particular wound dressings.
WO 00/32702 describes for instance a paper or nonwoven product containing fibers, filler particles or other particles produced by the layer-by-layer deposition of two interacting polymers, preferably anionic and cationic polyelectrolytes, which are typically used as dry and wet strength agents in the paper manufacture. Accordingly, this document also evaluates the tensile strength of the paper product.
WO 2005/032512 relates to an article comprising a particle, a first neutral polymer film and a second neutral polymer film which are associated by hydrogen bonding between a hydrogen bond donor polymer, such as polycarboxylic acid and a hydrogen bond acceptor polymer such as polyether, polyketone, polyaldehyde, polyacrylamide, polyamine, polyester, polyphosphazene or polysaccharide or a copolymer thereof. It is stated that capsules as one embodiment of this article are useful to deliver the core particle in a controlled and well-defined manner upon exposure to external stimuli. Application areas mentioned in this document are biotechnology, medicine, pharmaceuticals, foods, agriculture, perfumery, personal care and cosmetics.
US 2004/0137039 A1 provides in one embodiment a method of releasing low molecular weight polymers, such as drugs, dyes or other molecules from a LBL polymer film having a net excess charge, by introducing to the system at least one other type of molecule that binds reversibly to the film and thereby reduces the net excess charge. A second embodiment pertains to a method of selectively and reversibly releasing oligomeric and polymeric molecules, such as natural and synthetic polypeptides, oligo- and polynucleotides or other molecules having plurality of charges, from a LBL film formed from these oligomeric and polymeric molecules and a second polymer having the opposite charge, in response to variation in pH or ionic strength.
The controlled release of dyes from LBL films is also described in “A. A. Antipov et al., Sustained Release Properties of Polyelectrolyte Multilayer Capsules; J. Phys. Chem. B 2001, 105, 2281-2284” and mentioned in “M. Freemantle, Polyelectrolyte Multilayers; Science & Technology (2002), 44-48”.
US 2004/0047979 A1 describes an improved layer-by-layer-coating process for modifying the surface of a medical device preferably an ophtelmic device, more preferably a contact lense. Polyanionic and polycationic polymers are employed for this layer-by-layer coating which is said to increase the hydrophilicity of a medical device.
U.S. Pat. No. 5,885,753 discloses a self-assembled multilayer that can be effectively produced from two or more self-assembled monolayers on a substrate where each of the self-assembled monolayers is produced for a block containing a first functional group and a second functional group reacting with each other. Polymerized mono- or multilayer embodiments thereof can be employed in a variety of applications including photolithography.
WO 2004/07677 A2 relates to a continuous process for manufacturing electrostatically self-assembled coatings. Under background of the invention it is explained that such multilayer assemblies have found use in applications for full color flat displays, membrane separation, barrier coatings, corrosion control coatings, electrochromic coatings, electroluminescent devices, conducting and insulating circuits, optical and non-linear optical devices, solar cells, high strength composites and multielement chemical sensors. According to preferred embodiments of this method, layers of polycationic polymers and negatively charged inorganic materials, such as platelet clays are arranged alternately in layers having a thickness of about 1 nm.
U.S. Pat. No. 6,428,811 B1 relates to a thermally sensitised polymer-particle composite that absorbs electromagnetic radiation and uses the absorbed energy to trigger the delivery of a chemical. Metal nanoshells are nanoparticulate materials that are suitable for use in these composites.
WO 00/63115 relates to multilayer carbon nanotube films.
U.S. Pat. No. 6,861,103 B2 relates to a method for forming organic thin films on a substrate surface, preferably a silicon waver surface.
On the other hand, there is also one document relating to multilayer construction in diapers. WO 2005/023536 discloses an absorbent article comprising at least one first microlayer film region having a liquid intake function, at least one second microlayer film region having a liquid uptake and distribution function, at least one third microlayer film region having a liquid retention function, and at least one fourth microlayer film region having a liquid barrier function. These first, second, third and fourth microlayer film regions are co-extruded and assembled with each other to form the unitary micro-layered film system. However, these layers apparently have a thickness above the nm range and do not assemble themselves.
Controlled release systems utilizing a homogeneous (not-layered) matrix are also known and frequently encountered in the medical area.
WO 97/04819, as one example of this technology, relates to a medical device for controlling a bacterial infection wherein said device comprises a pH-sensitive polymer matrix containing a biologically active agent, said agent being released from said polymer matrix upon pH change. This matrix is homogenous and is not obtained by layer-by-layer deposition of two interacting polymers. U.S. Pat. No. 5,607,417 discloses a medical device for controlling a bacterial infection of a similar type as described in WO 97/04819.
WO 2005/013906 discloses a pH-responsive film comprising (a) a biocompatible, hydrophilic polymer that is positively charged at a first pH and in electronically neutral form at higher pH; and (b) an alkylene oxide polymer or copolymer. The film is obtained by dissolving all components followed by solvent-evaporation film casting. It has a thickness of about 3 to 6 mil and can be used for contraception, treatment and/or prevention of viral infections, treatment of vaginal infections, relief of vaginal itch, vaginal cleansing and enhancement of vaginal lubrication.